Radio beacon system



Jan. l5, 1952 W. J. OBRIEN 2,582,350

RADIO BEACON SYSTEM Filed Oct. 7, 1946 4 Sheets-Sheet l W. J. O'BRIENRADIO BEACON SYSTEM Jan. 15, 1952 4 Sheets-Sheet 2 Filed Oct. 7, 1946lNvlsN-rolal Jan. 15, 1952 w. J. o'BRlEN RADIO BEACON SYSTEM 4Sheets-Sheet 3 INVENTOR Filed OCT.. '7, 1946 Q W/LL/AM UT OER/EN l' BY V471' ,QA/EY.

Jan. l5, l952 w. J. o'EzRnEN 2,582,350

RADIO BEACON SYSTEM Filed oct. fr, 1946 4 sheets-sheet 4 234 236 B 238235 @M253 A #MP2/rm ,9M/unf i "205 f Daf/mf@ ...n n @fc5/vf@ 257 WM M;

It is a still further object of my invention to provide a beacon systemof the character previously referred to in which the receiving meansincludes a means for amplifying the phase difference between thereceived signals to permit the realization of extremely highsensitivity.

Other objects and advantages of my invention will be apparent from astudy of the following specifications, read in connection with the ac-4,

companying drawings, wherein: Y

Fig. 1 is a diagrammatic View representing the field pattern produced bytwo radio transmitters operating in accordance with the beacon system ofmy invention;

Fig. 2 is a geometrical diagram illustrating the mathematicalrelationships which define the phase relationship of two signals at Vapoint distant from the transmitters from which said sig- 1f nals areemanated; L1 n Fig. 3 is a vector -diagram illustrating kthe phaserelationship of signals emitted by theL two transmitters shown in Fig.1V;

Fig. 4 is a diagrammatic view illustrating the manner in which a fixedphase relationship may be established between two synchronised signalsof diiterent but harmonically related frequencies;

Fig. 5 is a schematic wiring diagram illustrating the equipment andelectrical circuits employed in one type of receiving equipmentparticularly adapted for use with the radio beacon system of myinvention; Fig. 6 is a vector diagram illustrating the operation of thatportion of the apparatus illustrated in Figs. 5 and 7 which functions todetermine and indicate the phase relationship between two separatesignals received by the receiving equipment;

Fig. 7 is a diagram similar to Fig. 5 but'illustrating a modified formof receiving equipment;

Fig. 8 is a diagram showing the geographical arrangement of thetransmitting and 4control equipment; and f Fig. 9 is a diagram showingthe details ofthe phase control apparatus.

Referring to the drawings, I have illustrated in Fig. 1 two radioantennae or other radiators of radio energy. These antennae are identiedby reference characters A and B and are indicated as being spaced fromeach other 'a distance S (see also Fig. 2). If the antennae A and B aresupplied with radio frequency currentlin such manner as to emitsynchronised signals of the same frequency and if the distance Srepresenting the spacing of the antennae A and Bis equal to onewavelength, there will be produced a eld pattern such as thatillustrated by the radial lines shown in Fig. 1.

Each of the radial lines of Fig. l represents the locus of all pointsalong which the phase relation at such point between the signalsemanated from antennae A and B is constant. The

numerical values indicated on Fig. l represent the phase relationshipbetween the signals when the distance S is equal to one wavelength andthe antennae A and B are voperated in phase with each other.

It will be noted by having reference that the lines of constant phaserelationship are straight except for that portion which is closelyadjacent the antennae A and B, these portions being of hyperbolic form.Actually the portions tong. 1

of the lines which have been indicated as. straight y lines are curved,being legs of hyperbolic curves.

Y respectively,- lines Rl and R2 "tennae A and B is increased.

Referring now to Fig. 2, I have indicated the antennae AandB as beingspaced apart a distance identi'ed'bythe dimension S. I have alsoindicated parallel lines Rl and R2 as extending fromy the antennae A andB. The represent lines drawn 'from the antennae AA and B, respectively,to an aeroplane P, such as the plane PI :illustrated in Fig. 1, situatedremote from the antennae A and B. When, as in actualpractice, the lengthof the lines Ri and R2 is large with respect to S, they may be assumedto bel parallel without introducing an appreciable error inthecalculations. If RI and Rzare mutually perpendicular to the line joiningthe antennae yA and B, then the lengths of Rl and R2 are equal.Consequently, signals emanated from antennae A and B at a given instantof time will arrive simultaneously at the plane PI and consequently thephase relationship between the signals received at the aircraft will bethe same as the phase relationship between the signals which areemanated from the antennae A and B. If, however, the aircraft be movedin a clockwise direction about the point 0 situated midway between theantennae A and B to a position such as that occupied by plane P2 in Fig.l so that the lines R3 and R4 extending, respectively, from theantennaeA and B to the aircraft makes an angle a with the lines Rl and R2, thelengths of R3 and R4 will be different. The distance R3 will beincreased by an amount indicated by the dimension line d at the left ofFig. 2, whereas, Vthe distance R4 will be decreased from the distance R2by an amount indicated by the dimension line d at the right of Fig. 2.It will be noted that S I d--2- sin a If the distances R3 and R4 areexpressed in wavelengths, then 360 S sin a.

:360 S sin a plus 0 The numerical values assigned to the lines ofconstant phase difference shown on Fig. l represent the values of p wheny and Fig. 3 is a vector diagram illustrating the phase relationshipbetween the signals received at an aeroplane P situated remotely fromthe antennae A and B under the conditions illustrated in Fig. l. Forexample, the two vectors AI and BI illusarea-,feto

trated as being in phase with each other represent theA phaserelationships between thesi'gnals emanated from the antennae Av and B-and also represent the phase relationship between signals received by aplane P, such as plane Pl, which i's proceeding outwardly along a lineof zero phase dierence (see Fig. 1). and B2v illustrate' the phaserelationship between the signals which are received by aplane- P2proceeding outwardly along the line along which- While I haveillustrated.. and described.. the

operation of the antennae. A and'. B under thev simple conditionswherein. S is equal to one wavelength and 9 equals zero, it willberealizedfthat S may be increased or decreased. as. desired: and,further, that the antennae A andB mayv be so operated that e hasfa.finite value other: than Zero. The. elect of so changing 0 from zero to.some other finite valueserves merely to assign new. valuesl 4:' to thelines representing the selected values of p indicated in Fig. l,lthesenew values fp' being equal to plus 6' where 0 is the finite valueof0 otherthan zero. Consequently a change in the value of 0 does notchange the shape of the pattern. illustrated in Fig. 1 but merely servesto` change the yvalue of a which is represented by a given lineA of thepattern. If, however, the distance S be increased, the pattern will bechanged in that the linesoi' constant phase dilerence indicated on Fig.1 will be crowded more closely togetherand additional lines will beadded to the pattern. Thus,

by increasing the distance S, the rate of change.

It will be realized that in order to, ascertain1 the phase relationshipat the location of' the plane P, the signals emanated from theantennaeAand B must be separately received at the location of theaeroplanes since if the signals are not separately received, the 'signalwhich will be received will be merely the vector sum of the separatesignals emanated from the antennae vA and B It will also be realisedthat where the distance R is extremely large with respect to thedistance S, it will be impossible to separately receive the signalsemananted from the antennae A and B by employing directional receivingantennaeon thev plane P. In accordance with my invention, therefore, theantennae A and, B are excited yat different but harmonically relatedfrequenciesl so that separate receivers carried by the'planes P may beused to separately receive the signals emanated from the antennae A andB.

The radio frequency currents which aresupplied to the antennae A and `Bare synchronized with respect to each other and are maintained in a xedmultiple phase relationship to each other. The` transmittingapparatus isillustrated in Figs; 8 and' and is described hereinafter: -I

Similarly, vectors A2.-

have.illustratedinV Fig. 4 the. manner lx1-which I the properly.synchronised operation of the antennae A and' B may be considered as'`maintaining a lixed multiple phase relation.

In Fig. 4 the sinecin've A." may represent7 the radio frequency-currentin the antenna A, whereas, the sine curve B' may represent the radioyfrequency current in antennaB. It will be noted'Y that, as illustrated,the-frequency of the current A is twicethatcf the current B'.Furthermore, the current B is illustrated as. lagging the'currentrAv byan electrical angle of9 measured; with respect to the frequency of thecurrentAf.. This relationship can be readily observed by. assuming afull wave. rectificatonof the current B whchv serves to. invert. the.negative loopsof the sine curve .and convert thenr to positive loopslindicated byidottedlinesf C in Fig. 4., It will'V be noted thatv thevpoints of. maximum4 current rep-f resented bythe curves B' and C lag`the. points of positive. maximum current represented byv the current Aby an amount equalto electrical degreesmeasured'with respect to thecurrent A. It will be noted that asimilar relationship exists betweenthe points of maximum negative current shown on the curveA' and theminimum or zero current. appearing on the rectilied curve.V B'C. Thusthe radio frequency current- B" whilebeing of one-half the .frequency ofthe current A' may be said to be in a. ixed multiple phase relation tothe currentA. and that this relation can be expressed as a; 90 phasedifference with respect to the frequency of the currenty A'. In Fig. 4 Ihave indicated bythe curve B the result of doubling the frequency. ofthe current B'. It will be notedv that the current B.' is` of the samefrequency as the current A'. and that it lags the currentA by 90electrical degrees.V

In. accordance, therefore. with my invention the antennae A and B- areexcited at different but harmonically related frequencies and aremaintained in multiple phase relationship to each other asdescribed.

While Fig. 4 and the description pertaining thereto has been based` onthe assumption that antenna B is operated at a frequency precisely equalto one-half the frequency at which antenna A is operated andwhile thelfollowing description of the receiving apparatusis based on the same.

assumption, itis vto be realized that the: essential featurev is that ofoperating the antennae A and B in synchronism witheach other,.atharmonically related frequenciesl and in fixed multiple phase relationto each other irrespectivev of whether the ratio of frequencies at whichthe antennae A and B is operated is equal to two or some other number.For example, if desired, antenna A can be operated at afrequency ofthree orfour timeslthe frequency at which antenna B is operated.

The aircraft P carriesntwo radio receivers, one tuned lto* thefrequency. of antenna A and the other tunedyto the frequency of antennaB. One of the receivers includesV apfreque'ncy doublingy stage whichserves to convert the received signal B' to thesignal B' of doublefrequency.l which double frequency is then the same as the signalA,receivedfroin the antenna A.` The ,separate outputs of the tworeceivers are then applied to an apparatus which functions to determineand indicate the phase relation between the currents A( andB". Thereceivers are so adjusted that an on coursef indication is providedIwhenthe planeRl is proceeding along the lineA A 7 I`1have illustrated inFig. one I receiving equipment adapted to operate in accordance with thepreceding description. In Fig. I have omitted the heater circuits forthe thermionic tubes employedas well as the circuits for supplyingscreen and plate potential to the tubes since these circuits form nopart of the present invention and sincethose skilled in this art wellknow the requirements for satisfactory supply circuits. The screensupply circuits are indicated by an arrow Yterminating in the legends-I-whereas the plate supply circuits are similarly indicated by arrowsterminating inthe legend B+. Y

The receiving equipment illustrated in Fig. 5 includes an antenna Iadapted to receive signals emanating from both the antennae A and B, thereceiving antenna I. being connected in series relationship through theprimary winding 2 of an input transformer 3 and the primary Winding 4 ofan input transformer 5, the lower end of the winding 4 being connectedtoground as at 6. The input transformer 3 supplies a Yradio frequencyreceiver tuned to the frequency of the signals emanated from antenna B,whereas, the input transformer 5 supplies a second radiofrequencyreceiver tuned to the frequency emanated by antenna A.

The input transformer 5 includes a secondary 4form ofwinding 'I which isshunted by a variable con- A denser 8 permitting the circuit to be tunedto the frequency transmitted by the antenna A. The output of thesecondary 'i is applied between the grid and cathode of a thermionictube 9 whose plate isconnected through a coupling condenser III to thegrid of a subsequent amplifying tube II. The plate of the-tube 9 isconnected to B-I- through a plate inductance I2 which is preferablyshunted by a resistance I3.

The output of the tube II Yis coupled to the input of a tube I4 by aninter-stage coupling similar to that previously described, whereas, theoutput of the tube I4 is applied to a coupling transformer I5, theprimary of which is shunted by a resistance IB and the secondary ofwhich is tuned as Vby a condenser I'I shunted by a resistance I8, thevoltage developed across the resistance I8 being applied between thegrid and cathode of a fourth amplifying tube I9.

Grid bias'voltages for the tubes 9 and .I9 are preferably developed bymeans of resistorsv connected in series with the cathodes ofthe tubes,these resistors being by-passed in the conventional manner by condensers2|. A portion of the grid bia-s voltages for the tubes II and I4 aresimilarly developed by cathode resistors 22 by-passed by condensers 23and also by compensating resistors 24 connected in series between thecathode and the resistors 22 but not provided with by-pass condensers.-This form of cathode circuit is employed to maintain phase stability inthe stages including tubes II and If and forms a part of thesubject-matter disclosed and claimed in my copending application, SerialNo; 495,496, filed August 5, 1941, Patent No. 2,404,809 issued July 39,1946, and entitled Compensating Circuit.

The remainder of the grid bias voltage which is applied to tubes II andI4 is obtained by connecting the grids of these tubes through gridresistances 25 and 26 to an AVC bus 21 which is supplied with a Vdirectcurrent voltage whose magnitude is caused to vary with the strength ofthe signal'picked up by the antenna I'A in-a manner to be hereinafterTdescribed. Preferably as, the channel previously vdescribed -r cause ashift inthe phase of This, resistance serves also' an isolatingresistance 28 is interposed betweenthe resistance 25 and the bus 21 andthe lower ends of the resistances 25 and 26 are each preferablyby-passed to ground bymeans of condensers 29.

ftion. On the other hand the tubes I'I and I4 are provided with avariable grid bias and consequently operate to provide a variableampliication. of the signal.Y Since variations in the amplification of.the tubes II and I4 will tend to thesignal amplified by such tubes, thecathode circuit previously referred" `to is! employed to reduce thisphase shift to a minimum.

The input transformer 3 previously referred to i includes a secondarywinding 3l! which. is tuned by a variable condenser 3| to the frequencyemitted by the antenna B, the output of the transformer -3 being appliedbetween the grid and cathode of an amplifying tube 9.

The output of the tube 9 is fed through tubes II', I4 and I9', allconnected in a manner substantially identical with that previouslydescribed in connection with tubes 9, II, I4 and I9 with theexceptionthat the circuits are tuned to the frequency emanated from theantenna B, Wherein detail is tuned to the frequency emanated by theantenna A.

In choosing the constants for the various circuit components of the tworeceivers, the tuning capacitiesin each channel are preferably madeequal, whereas, the inductances employed in the channel for receivingthe lower frequency emanated from the antenna B are made four times thatwhich is employed in the high frequency channel for receiving thesignals emanating from the antenna A.

The Q of the tuned circuits; that is, the ratio of thereactance to theresistance is so adjusted that the Q for the low frequency channel ishalf that of the high frequency channel. By adjusting the `constants inthis manner, the-phase shift 'produced by one channeiwill be compensatedby the phase shift :produced in the other channel. A preference isexpressed for the use of' high inductance and' low capacity coupled withaV low Q and a low amplification per stage for the purpose of reducingthe phase shift which may'result from'changes in temperature, changes intube capacities and changes resulting from the variable amplication ofthe tubes.

Accordingly the plate inductances I2 which are shunted bythe resistancesI3 and IB are made of a size sufficient to permit the intercoupled plateand grid.' circuits to be tuned to resonance by the internal plate tocathode and grid to cathode capacities ofthe tubes. The Q of the highinductance circuit is reduced by employing the shunt resistances I3 andI6 for the purpose of improving the phase stability of the amplifier. tobroaden the tuning and resort is therefore'h'ad to the use of arelatively'large number of vlowl gain stages to provide'the necessarysharpness of tuning and the necessaryampliiication. Furthermore, it isdesirable to use a relatively low gain per stage since the phasestability in a low gain amplifier is superior to that of a high gainamplifier.

1 Theoutput of the tube I9 is coupled by means gf aseupliasirassfgesf,32 te a. 'frerlsncy C1011- accesso bling stage .employing tubes 33 andv34, the. plates of which are connected in parallel and to 'the primaryof a coupling transformer.. 'The frequency doubling circuit employingtubes and 34 is of conventional construction, the grids/of the tubesbeing connected torop'posite en dsof a center tapped secondary 3,6 ofthe .transformer 32 so as to be supplied With grid voltages which areout of phase with each other.

The tubes .are biased substantially to cut. on 4so that Yplate currentflows in Vthe tubes only during such time as a positive signal isapplied Vto the grids of the tubes. Since the platesof vthe tubes are inparallel, the vfundamental andy odd harmonics are rejected, whereaslgtheeven harmonics are applied to the primary of the transformer 3.5. Thesecond harmonicA appears lat a much .higher amplication than .do thelhigher evenharmonics so that by tuning the: 'secondary 3'1 of thetransformer 35i as by means'oa condenser .38, the voltage winding 37 maybe caused to consist alrnost'enappearing across thev v xyindings 4,1and48 having their adjacent terwindings 47 lfminalsfnterconnected as bya condenser and 'gr'ffounded as at 50. The opposite terminals-ofthe .and48 arejconnected, respectively, to the cathodes of rectifying tubes 'Tland T2.

The secondary comprising the windings `V`4'! and 4 8 maybe tuned tothejfrequency impressed upon thel primary 40as by means of` a variablecondenser 5 In. a similar manner the transformer 4l' inmefwinding '.52is connected rto ground yas by 'means of a conductor 54 through acondenser tirely of the second harmonic which is, ofcourse,

a .frequency twice 'that which is ,applied tofthe input of the amplier.

Similarly, the tube I9' is cou-pled to a k'f'requency quadrupling stageemploying therm'ionic tubes 33' and 34", Vthese tubes being coupled 'toan output transformer 35' Whose secondary 31 is tuned to a frequencyfour times that which is applied to the input of that amplier.v Thus thetransformer secondaries 37 and v3'1' develop radio frequency voltages ofidentical frequencies since these voltages are, respectively, two timesand four times the frequency emitted by the antennael A and B and sincethe frequency emitted by an# tenna A is twice that emitted by antenna,.B.

These voltages of equal frequency which are developed by the secondaries37 and 3l'. are applied, respectively, to amplier tubes 39' 35' Whoseoutputs are connected, respectively1 .tov-f tuned primaries 40 and 40'of output transformers 4| and 4|. Each of the tubes 39 and 33'preferably include also 'a rectifyin'g circuit for developing thepreviously mentionedrAVC `voltage. f

accordingly connected to the plate of the tube through a condenser 42.The radio frequency voltage is thus applied 'to the diode `element ofThe diode element of `the tubes F39 yand 39' are theL other terminal isconnected to the {anodesl of the rectifier tubes TI and TZ, whichanode's are. connected in parallel with each other. A resistance 56 isconnected betweenthe conductor 54 land ground .and a resistance '51 isconnected 'between the conductor 54 and the Vinner terminalgoftherwinding '41. lThis same inner terminal'of the Winding 41 isl alsoconnected as bfyineans of a `conductor 58 through a blocking vresistance59 to the grid of a thermionic tube 60. 'The circuits just 'describedincluding the rectifier tubes .'Il vand T2 operate to apply to the'gr'idof the vacuum tube T60 a .direct currentv potential, themagnitude andpolarity of which is a function of the phase relation between thevoltages appearing across the 'transformer secondary vwindings 41-48.and 52.

The operation of these circuits can best .be

described by having reference vto Fig. 6 by employing the voltagedeveloped across the Winding Q52 represented by reference character 'EBas a reference voltage. l The `voltage EB is represented in Figo bya'vector designated `by the .reference character EB and `disposed in aposition representing a phase dispositionof zero degrees. If 'thevoltage .developed across the winding 4'!v is in phase quadrature Withrespect to the voltage developedacross ,the vWinding 52, then thevoltage 1 which is applied to the lcathode of the tube Tl with respectto ground may be represented by the pliedrto the 'cathode of T2 the tubeand serves to :produce a rectied a-current flowing from :the diodeelement'to -Athec'a'thode, from thence to ground and from groundthrougha diode .droppin-g resistor 43.

The direct current voltage developed lacross the resistor 3 serves toplace the .diode element at a negative potential with `respect to'.ground,

A the magnitude of this 4potential depending upbn the magnitude .of vtheradioffrequency voltage which is applied .to the diode element. vThediode element is, therefore, lconnected .to 'the AVC bus 2'! throughresistances 44 and 45, the mid-point of which is connected to .groundthrough a condenser 46, the resistanc'es 44, 45 and -the `condenser 46cooperating to .exclude radio frequency voltages from the AVC bus 2l. isconnected tothe grids of the tubes vHand 14, the ampliication of thesetubes varied inl a well understood manner in accordance-with thestrength of `the signal which developed at the 'plate of the tube 39. Anidentical circuit lis employed for controlling the tubes H' and 14 inaccordance with the lvoltage developed bythe `tube 39'. A

The transformer 4l includes two `secondary Since *thisA bus .appearing-between the anode ,is represented by the vector Ee,'this sum beingrepresented in Fig. 6 by the vector -l-.EA and leads the voltage EB 4byan angle X '.equalling 90. Since the voltage which vis apand generatedby the Winding 48 must be 180 out of phase with respect to Vthe voltageapplied to the cathode Tl, the voltage applied to the cathode T2 may bevrepresented'by the vector 'EA which lags EB by Thus the voltage andcathode of Tl sum of -l-EA and an angle Y which equals vector En.Similarly, the voltage which is applied between the anode and cathode ofT2 is the vector sum of -EA and EB, this resultant being indicated bythe vector Erz in Fig. 6.

It' vvill be noted that Eri is equal `in magnitude to Err as long asangle X is equal to angle Y for 'the reason that -l-EA must be alwaysequal and opposite to V-EA.

The resistance 5l is connected in the .cathode circuit Vfor TI while theresistance 56is connected inthe cathode circuit .for T2. 'Ihese re-Ysistan'ces are of vequal magnitude with the result that the voltagedrop produced in V.these resistances by the direct current flowingthrough the tubes Tl and T2 Will be equal. It will be noted that theresistances 56 and 51 are connected in series, the free end ofresistance 56 being grounded and the free end of resistance 51 beingconnected to the conductor 58. Thus .the direct current "which caused toflow through potential, so that the and Erz. angle Y', result that a.direct current of greater magnitude 2,582 suo the resistances 56 and 51is caused to flow from the Afree ends towards the interconnected endsthereof. Thus, with respect to the point of interconnection of theresistances 56 and 51, the grounded end of the resistor 56 and theconductor 58 are both raised to an equal positive voltage of theconductor 58 with respect to ground is zero.

Otherwise stated, since the grounded end of resistance 56 is maintainedat a fixed or zero voltage, then the point of interconnection betweenthe resistances 56 and 51 may be said to be depressed to a minus voltagewith respect to ground, whereas, the conductor 58 is maintained atground voltage. Thus, it Will be noted that the fact that conductor Bisl at ground potential is indicative of the fact that the voltagedeveloped across the transformer winding 52 is in phase quadrature withrespect to the voltage developed across the transformer windings l1- 48,

Assuming now that the voltage across the winding 1 -.48 shifts clockwisewith respect to the voltage across the winding 52. The voltagerelationships under these circumstances are represented by the dottedvectors .in Fig. 6. It will be noted that the potential applied to thecathode of the tube TI is represented by a vector -i-E'A which leads thevector EB by an angle X' less than 90. Similarly, the'voltage applied tothe cathode of T2 is represented by the v-ector -E'A which leads EB byan angle Y greater than 90. rThe resultant voltage which is appliedbetween the anodes and cathodes of the tubes TI and T2 are indicated,respectively, by the vectors Efri Since the angle X' is less than theE'Ti will be greater than ETz, with the will flow through Tl than willflow through T2.

` The direct current voltage developed across the resistance 51 willvexceed the direct current voltage developed across the resistance 56 sothat the conductor 58 will be shifted positive with respect to ground.

1n a similar manner, if the voltage developed across the transformerwinding 41-48 were to be shifted in a counter-clockwise direction fromthat illustrated by the solid lines in Fig. 6, 'the conductor 58 wouldhave been shifted negative with respect to ground. Thus, phasequadrature relationship between the output voltage of the tube 39 andthe output voltage of the tube 39 is represented by zero voltage on theconductor 58, whereas, a phase ang-le of greater or less than 90 betweenthe outputs of these two tubes Will be represented by a negative orpositive voltage being developed between the conductor'58 and ground.

For the purpose of providing a visual indication to the pilot of anaircraft carrying the above described receiving equipment, I employ asensitive galvanometer 6I which is connected in a bridge circuit toprovide an extremely sensitive indication of voltage ohangesof theconductor 58 with respect to ground. It will be noted that thegalvanometer 6| is connected in the position of a balanceindicatingdevice in a Wheatstone bridge circuit, one leg of whichcomprises resistances 62 and 63 and the other leg of which comprises aresistance 64 and the plate to cathode resistance of the tube 60.Voltage for operating the Wheatstone bridge is supplied from B+ througha resistance 65 to the point of interconnection between resistances 62and .64, the negative return being from the point of interconnection ofthe cathode of the tube with the resist@ 12 ancev 63 and through aresistance 66 to the ground. Y u

The resistances 62, 63,65 and 66 are so adjusted as to applya positivepotential with respect to ground to the cathode of the tube 66. The gridof the tube 66 being connected to the conductor 58 is normallymaintained at ground potential. This serves to bias the tube 60negatively and the magnitude of this bias is arranged to lie on thestraight portion of the grid voltage-plate current characteristic curveof the tube 66. Furthermore, the resistances r62, 63 and 65 are soadjusted with respect to the plate resistance of the tube 66 when the'grid thereof is at ground potential as to provide zero voltage acrossthe galvanometer 6 l.

The galvanometer 6I is preferably a Zero center instrument and somaintains its indicating needle at a central position on its dial whenthe conductor 58 is at ground potential.

If the phase relation between the output of the tubes 39 and 39 shiftsfrom a p-haselquadrature relationship, the voltage applied to the gridof the tube 60 will be either positive or negative with respect toground, depending upon the direction of phase shift. This will serve toeither decrease or increase the plate to cathode resistance of the tube60 and will accordingly cause current to ow in one direction ,or theother through the galvanometer 6i. Thus, a deflection of thegalvanometer needle in one direction indicates ajphase angle of lessthan 90 between the outputs of the tubes 39 and 39', whereas, a swing ofthe galvanometer needle to the left indicates a phase angle between theoutputs of these tubes of greater than 90.

Reference has been hereinbefore made to the use Vof vthe above describedreceiving equipment for apprising the pilot of an aircraft carrying thesame that he is or is not following the course indicated in Fig. 1 by Inorder for the zero center indication of the galvanometer 6l to indicatethis condition, it is necessary that the signals which are passedthrough and 'amplified by the low frequency channel of the receiver beshifted 90 with respect to the signals which are passed through andamplified by the higher frequency channel of the receiver.

Accordingly, I connect a variable condenser 61 in parallel with thetuning condenser 3 I associated with the input transformer 3. Adjustmentof thecondenser 61 serves, of course, to detune the tuned circuitrepresented by the winding 30 and the rcondenser 61 so that in order toshift the output of the tube 39' 90 with respect to the output ofthetube 39, it is only necessary to produce a phase shift in the circuit30--3l of 22%".

It is desired at this time to point out that while .L nave described thelow frequency channel as being provided with a quadrupler 33t', and thevhigh frequency channel as being provided witha frequency doubler 33-34,the frequency y* doubler may, if desired, be omitted from the highassassin *13 frequency vchanneland 'a frequency doubler employed in thelow frequency channel 'instead of the frequency quadrupler. Theessential requirementis that thefrequ'ency multipliers be soarrangedthat the signals which are emanated from the antennae A and B beconverted into identical frequencies before they 'are applied Vtothefphase determining apparatus. In this connection it is desired topoint out that phase difference between the signals emanated fromantennae A and B is multiplied by and to the same extent 'as' thefrequency is multiplied by the frequency multiplers employed in theamplifier channels. Thus, by additionally multiplying theirequenciesbefore they are applied to the phase determining apparatus,an increase in sensitivity of the indication maybe obtained. Y

Briefly summarising the operation ofthe above described equipment, theantennae-A and B- are supplied with radio `frequency currents which areof different but harmonically related frequencies `and which are in ayfixed multiple phase relation to each other. The energy emanated fromantennae A and B is picked up by the lantenna I l and applied to theinput transformers 3 and 5. r One channel of the receiver operates to.receive,

amplify and double the high frequency emanated from the antenna A,Whereas, the other channel serves to receive, amplify and quadruple.thelow frequency signals emanated from 'antenna B. Furthermore, thislow frequency channel serves to shift the phase of the received signals90" with respect to those passed through the other channel so that whenthe multiple. phase relation between the signals from antennae A and Band received by the receiving antenna l is I the output voltages of thetwo channels will; be of identical frequency and. in phase quadraturewith. respect to each other. This, through the action of the rectiers TIand T2 and the amplifying tube SI1, will serve to provide a centerindication on the galvanometer 6|.v

Should the pilot wander from the line the phase relation between thevoltages applied to the phase determining portion of the apparatus willbe correspondingly shifted and the galvanometer will swing to one sideor the other to indicate to the pilot not only that he is 'oi course,but in which direction he must fly in order to again arrive at the oncourse line Thus, the system just described operates to. provide for thepilot of an aircraft a continuous indication of his position withrespect to the desired course.

It will be further noted particularly by having reference to Fig. 6 andcomparingl the magnitude of the vectors -EA and -EA with the vector EBthat the system is substantiallyV independent of the relative magnitudesof the signals lemanated from the antennae A and Band receivedl bythereceiving equipment. This makes itv substantially impossible to renderthe beacon useless byv deliberate enemy radio interference.

Referencev has been made hereinbefore toy the desirability of providinga, systemv wherein. the course along which the. pilot will-be.. guidedby the operation of the device. can be selected at will. I haveillustrated. in Fig.v 7 a modied form of receiving equipment which isparticularly adapted for such operation. The circuit illustrated in 14Flg.'7 is identical to' the circuit illustrated 'in Fig. `5 with theexceptions which are hereinafter noted.

It will be noted that I have connected the grid and plate of the tube I9each to ground through variable condensers 68 and 69. These condensersoperate in the same manner as has been previously described inconnection with the condenser 61 to detune the grid and plate circuitsofthe tube I9' and thus to produce a phase shift in the signals passedthrough such circuits. The condensers 68 and 69 are preferably mountedupon a common shaft 'l0 which carries a pointer ll Yadapted to bemanually moved over 'a dial or scale 12. Y

The scale 12 is preferably marked Ain values of c and the calibration'isypreferably so arranged that-When the pointer 1l vis tuned to indicate-apredetermined value of o, the galvanometery 5l will indicate zero whenthe plane is on the course line along which d has that predeterminedvalue.

As was previously pointed out`in vconnection with the operation of thecondenser B1, the amountof detuning which is effected by the condensersB8 and 69 need be but very little. For example, if the scale l2 is tohave an'adjustment range of 180, then the botal phase'shift need only be45 since the phase shift is quadrupled in the quadrupling stage. Since'this phase shift is effected simultaneously in the grid circuit and inthe plate circuit of the tube I9, each circuit need only be shifted22%". This amount of phase shift corresponds to a negligible amount ofdetuning of these circuits. I

I have illustrated also in Fig. 7 certain calibrating equipment whichmay 'bev employed in conjunction with the adjusting condenser'l toeffect such phase adjustment of the receiver as may be necessary tomaintain exact correspondence of the reading of the pointer ll on thescale 12 with the actual value of `qs at which the galvanometer 6Iindicates an "on course condition. This calibrating `equipmentpreferably includes a sui-table high frequency oscillator indicatedgenerally'by the rectangle carrying the reference character 13. Theoutput of the oscillator 'i3 is coupled by means cfa transformer 14 toafrequency doubling stageincluding vacuum tubes 15 and 16. The plates ofthe tubes 'i5 and 76 are connected to each other lby a conductor 11 andthe tubes l5 and 16- are biased substantially at cut oir so that thevoltage developed on the con ductor 'l1 with respect to ground containsa high "percentage of voltages of vdouble the frequency fand' also fourtimes the frequency which is 'genera'ted by the oscillator 13.

The conductor 11 is connected toa conductor '8 through 'a filterarrangement including condensers 19, and B-- and resistances 82, 8'3 and84. This filter is adjusted to attenuate the second harmonic to agreater exten-t than it attenuates the fourth harmonic so that theconductor T8 will be provided with a second harmonic voltage and. afourth harmonic voltage of substantially the same voltage.

The conductor 'I8 is connected to a pair of stationary switch points and86 which are adapted to be engaged by a pair of switch arms 8l and 8'8.The antenna I' is similarly connected to a switch point 89 While thearms 81 and 88 are connected Ato the primaryy windings 2 and 4 of theinput transformersl 3 and 5 in the manner previouslyl yartefacto -re,'ofcourse, fed to the amplifier inthe manner previously described inconnection with Fig. 5. When the switch is turned to a posi-tion inwhich the arm 88 contacts the point 85 and the arm B1 contacts the point89, the voltage on the conductor 89 will be applied to the input of thereceiver along with the voltages picked up bythe antenna I. Y

The frequency at which the oscillator 13 operates is so chosen that thetwo frequencies appearing on the conductor 18 are substantially equal,respectively, tothe frequency emanated by the antennae A and B. Thus,when the output of the oscillator 13 and the antenna are both connectedto the receiver, the beat frequency resulting from the mixture of thesetwo sources of energy will be indicated by a fluctuation of the needleof the galvanometer 6|. The oscillator frequency is then adjusted toprovide a substantially zero beat and the antenna switch is then movedto a third position in which the arm 81 contacts the point 85 and thearm 88 contacts the point 86, thus serving to connect the receiversolely to the output of the oscillator 13. The

pointer 1| is then moved to a predetermined point on the scale 12, suchas the point marked by the reference character 12. The adjustingcondenser 61 is then adjusted to give an on course indication on thegalvanometer whereupon the pointer 1| will accurately indicate on the.

scale 12 those -valuesof o at which the galvanometer 6| will give an oncourse indication when the phase relation between the signals receivedfrom antennae A and B is represented by that value of c.

The location of the predetermined scale indication 12 is determined byexperiment and is that point at which the represented value of is equalto the fixed phase relation between the two frequencies developed by theoscillator 13 and doubler 15--16 and applied to the conductor 18.

The phase relation between the second and fourth harmonics of theoscillator 13 is a fixed and constant relationship and once determinedthat phase relationship can be used to determine the location of theCalibrating mark 12. Thereafter, the receiver may, of course, beadjusted to render the readings of the pointer 1| on the scale 12accurate with respect to the on course indications given by thegalvanometer 6|.

It will, therefore, be observed that I have provided in the apparatusillustrated in Fig. '7 a means whereby the pilot of an aircraft maymanually move the pointer 1| to a position on the scale 12 indicatingthat value of which corresponds to the course desired to be followed bythe plane. After this adjustment is made, the galvanometer 6| willoperate in the manner described in connection with Fig. to indicate anon course location of the plane and also to indicate to the pilot whenthe plane wanders from the desired course and in what direction it willbe necessary to ily the plane in order to bring it back on the desiredcourse.

It will be realized, of course, that for convenience it will probably bepreferable to. calibrate the scale 12 in terms of the compass directionof the various courses indicated by the eld pattern lines illustrated inFig. 1 so as to avoid the necessity of translating a given compasscourse into a given value of o and then to set the pointer 1| to thatvalue of qb. If the scale 12 is properly calibrated, it may be turned toa point indicat- A ing the desired compass direction of the course,

`mitter 204 may comprise a in shunt across `transmitting controlapparatus 202 2 05 associated, respectively,

.'ployed to connect the cables of conventional equal to the surge lines201 and at which time the galvanometer 6| will indicate an on coursecondition when the plane is following that compass course.V

Reference has been made hereinbefore to the necessity of maintainingfixed the multiple phase -relation between the signals radiated fromanconnected to transmitting control apparatus 202 line 203. The isemployed two transmitters 204 and with antennae B and 201 and 208 may beemtransmitters 204 and 205 with the control apparatus 202, or if desiredsuitable radio frequency transmitting and receiving links may beemployed in lieu of the metallic transmission lines.

Fig. 9 illustrates control apparatus.

as by means of a transmission to actuate and control A. Transmissionlines in detail the transmitting As shown therein the transpoweramplifier whereas the transmitter 205 may comprise a power amplifierexcited from a frequency doubling stage so that the frequency of thesignals radiated from antenna A will be twice that of the signalslradiated from antenna B. The transmitters 201|V and 205 are .eacharranged to be excited by radio frequency energy developed in a suitableoscillator or similar source represented by a rectangle bearing thereference character 206. The transmission lines 201 and 200 which conveythe energy from the oscillator 200 to the amplifiers 204 and 205 maycomprise co-axial construction as shown, or may comprise other suitabletypes of radio frequency transmission lines. Y

The outlying end of the line 201 is preferably coupled directly to theinput of the amplifier 204 as by means of a coupling resistance 200.Similarly a resistance 22| may be employed as the coupling element forconnecting the transmission lines 208 to the input of the frequencydoubier stage included in the transmitter 205. The resistances 209 and22| are each preferably made impedance of the transmission 208. In asimilar way the input circuit for the transmission lines 201 and 208 maycomprise resistances 221 and 220 connected the transmission linesbetween the central conductors 229 and 230 thereof and the outergrounded sheaths 23| and 232 thereof.

The oscillator 206 is coupled to the transmission lines 201 and 208 asby extending one supply ductor 234 to the centre conductors 229 and 2301l through a pair of identical tank circuits 235 and `ble to realizeanydesired..multipleiphaser a.-

.Sioii't.e'eiies,1ieid type iiiciiidiiife Seri `terminal of which` w esat zas. The free end termiiidtcf-eeth 0f ,he

iet, eechiiicipdipe enfiiiducteiice.zelanda ...tee-ine .ttpeeeecdiifeetly throiieii-.ttiereceiie shunt-ooiiiiectedcorideiieee238- ..1employaiso .c pheec eiiiftiiiecoiideiiccioiftlie split stator veriebictype., .tectiiiorelcieei- .ont 239 .thereof-beine coiiiicctedtoetiiee911@ tot v231iV while oneof the .stdtoi'f'POriiQti .250 nected .totheooiiddctor@ and; tite cthe` portion zeide connectedtc the coiitiiiticWhen` themovepie eiemepteee occdpiee. e-.cepdie .iifi'e 0: the 'oppositedirectiony tialposition,A tigetunins ofthe remedied. .Se 1.o iiieewitcharm Ztl'to engage tile .othei act. and zasffwiu-be ideniicai sachet the,yo ages iic ioiegfoiogiiwjiii be noted ihatiyiien developed across lthe.resietencee 22.1 dii @twill ittiiig epiidretiieieo operating esto beinopvhase with eachother. v '4 4 v.theline210i! through the receiving,anmovebie elementitewili detiiiiet. et oI liegewilibeeppliedtc the ter235`ina directionopposite toothw .det aigle .condenserelement 239,',wi11teiikcircuit 236,with theieeiiit' et e. S ,new y.iioiititc1-2-iifiithe-event. there ocoi the Voltage develeped ecieesetiiere Weecdr,lecieeeiiepeeid-coiiditio'neeerrine toeiiift 221 will shift in onedirectionvvhereas the oltthe compass direction of the line 200, thechang.- eeedeveicpedecroeetiie resistance 2.38 ift .ide detect. .ef-thcieceiviiie-epperetiie will detuin the opposite .direeticc- .Thusebyproperly l2.o etetiie iwitciiiiie ended? positioning the iiiovdlolelemetititd itis pQS- 'meter movement 5125.8 ,is eo.

tie' ehii iitgeftiie teeeivecwill .be f. anced switch armlfiLto eng tionbetween the two radio .frequency sie 1S tto. ceueetiietlehiit in phasewiiiehojpwiii rige emanating from antennaeA and c 4 vss direction of theline 2 00 backA tovvardits In order that .the position of,tlrcfmova-lole` ele- 2 5 Vvorigl'rialu.position. ment 2.39 mayv be automatically`controlledpto Emile-.fthe phase control apparatus hfzsfoe'eri maintainthe desired multiple-phase relationbedescribed with reference to pos'ioning the oontween the radiated.signalsI IconnectthelmovtrolreceiveralcngItloelineZQvvitl; atieVY element. zoetea-euitepiedeivioe..mechedei n ism which mamas shownin Eig.y 9,.comprise a 3o Y' it is .to.be realised,that.etiier.phase lilies may 'be .liieedior control b'ypoperlddiii tmentof the bled with, telfreversible yelectric motor 242.vrThe -motor- 262 may be ofenyisditable reversibie-.itvpefbpt the oneAWnienis illustrated in' Fig.' .deompiiss a reeiveresweehereiiibfeforel.deson.l o l 'nidgw'inderencetdlifig.- 7- Tliiisfii Willweeen that le ings 243 analisi, sey arranged that it'iiejdieeooiltitoirece'iyerooeactewithtiiemotoiited .ee

` .ltliitiiig ediiitiiiientfto maintain ,the .cours `.clefiinedloy t .eoperatiopoftiie. odio loeacoiieye- `teni..e'x. t. eiided Vat .anydesired compass. diie'otion irreepectiveofdistiiibineinline ,eser .ext

n10-1.501' 'snergsd by POWSI' .lpldgthmugh one of thevfields, thedirection :Ntrotatio l v opposite to that resulting-trom the applic f`Aof power through the other-neld. A i n oner terminal of ,ihe'moiozeg maybe e911- 40 conditions tending t cause a S. iitoithedeiined nected to asuitablesource of power Yillustri''ted /QQHTSS .I Ov di@ .90mm/5.5Qirtpfif Ain Fig. 9 as comprisingV a battery'L Z'githeotnier v' g. @iidDlia@ .CQIiYQl tpprlis ey be eoiinectedto-erodiidclaimed,hereinfisdieclosed.

in my copeiid eeppiioetieiierial. No. 45.43B; fiiled v'rfil .i3lQZQBet'teiitNO- 244.9474 `ist.ded...Septein eri 9&8, entitledadiomttiiie'sysltem. d edii/lisiodtiieieoi 'Serial ;No.. 299,023, iiled@tombera 1.9.4.3. new aneld windings 243 and Zqifis-exteiiddlbyf ofcontrol conductors ,Zland-Mato e` right hand contactsfi v:an 250, respofy a controlswitch whichincludesaibala switch arm 25| whicnisin turn(conne 501e. on' System.

ned and eri...it.1.e.d fRedio Frcdiieiicy ground as bymeans orconductorl'e'z. -V M The control. switch just described isoprer'ferablylocated at or near a receiving apparatudsy`v20lhand the controllconductors `24H and- 248 .comprise he control circuit showndiagrammatically; Vzit/[21123 Figa. `The receiving apparatus whichisshowngen erally at 29| in Figs'. 8 kand Q-pIeferably a receivingantenna R, vlocated ,onfltheline and connected to the inputk cfareceiving: ,appaictus Such es .hes loeren hereiiibeicie fdeeriiced Withreference to, Fes- .Seite 6.- In. tnosefiieures the output of thereceiver iS .shown asbeing .ap-

plied to a galvanometer el for providinga visual .for hyperbolic.Surfaces .which.edriecesicomprise alternating. velectrical.equivocan-displacement c5 ,surfaces- Wiiere reference iodey beenmededele- Froi theI V.foregoiiig .itwill .be observed. that. I haveprovided a radiobeacon system, which operates to generate a eld patterncomprising. radi- .elly outward. extendida ,lines .comprising .the locus55 .offalipcintc of predeterminedfphlase relationship between .Signale.transmitted from two 'or more .adtewee While I havekin theforegoing,referred to the sfield.

patientes comprising. lines 4of. equi-.phase eo relations/hielt will.loeceporeoidted that these ffiines..ectua11y represent; a .horizontal.Sectionoi thenelwliich eld is in Vreality characterizedinbenfi'?..fQfgguiepliase lines referenceI is intended .to tlfiat.portion` of thel equi-phasfe-dis- .pldcemeptsuriace .alone .whichYtheeircralf. or

other .vehicleis proceeding.

7o I t Wiiibe furthermore observed that thesys.-

tem of my .invention .includes .receivingV ediiipmentpermitting,thesesignals to. be separately received and Lpermittingtheirphese reldtioiito bedetermiiiedand indicated` ori' an .indicatingflinstrument in terms of the position of the plane 'with respect to thecourse desired to be followed.

Y Attention is directed to the fact that the operation of the system isalmost entirely independent of relative magnitudes of the signals, thusmaking it extremely difcult for the enemy to render the systemineifective by means of deliberate radio interference.

It will also be noted' that the system of my invention may be used toguide an aircraft in any selected compass direction and that the courseto be -followed by the plane can be determined by adjustments madesolely in the receiving equipment carried by the plane incontra-distinction to the present commercially used equi-signal systemswherein a change in course exceeding or can be effected only by changingthe geographical location of the transmitting antennae.

Attention is further directed to the fact that the use of the Wheatstonebridge type of indicating circuit for the galvanometer 6l makes thegalvanometer inherently extremely sensitve to changes in output voltageproduced by the phase determining portion of the apparatus. Thisprovides for an extremely sensitive indication permitting the pilot ofthe aircraft to closely follow the desired course.

Furthermore, since the magnitude of the control voltage which is appliedto the indicating circuit is determined by the magnitudes of thevoltages applied to the rectifier tubes TI and T2 and the phaserelationship between these voltages, it will be seen that additionalsensitivity may be obtained by additionally amplifying the signalsbefore they are applied to the rectifier tubes. This result cannot berealized with the equi-signal systems ywherein the distinguishingdifference between the two received signals is a proportional differencewhich cannot be altered by an amplification of the signals.

While I have, in the foregoing, referred particularly to the use of theAradio beacon system of my invention as a navigation aid for aircraft,it will be realized that the beacon system may be used with equallyadvantageous results to guide other forms of vehicles or conveyances,whether operated on land or on water.

While I have shown and described the preferred embodiment of myinvention, I do not desire to be limited to any of the details ofconstruction shown or described herein, except as dened in the appendedclaims.

Iclaim:

l. The method of guidingV a vehicle along a selected course whichconsists in simultaneously radiating from spaced locations synchronisedradio waves of different but harmonically related frequencies having afixed multiple phase relation to each other to define a locus of pointsof predetermined multiple phase relation between said synchronised wavesand coinciding with said selected course, separately receiving at saidvehicle the waves from each of said locations, multiplying the frequencyof one of said separately received waves to provide twoA radio frequencysignals of identical frequency, comparing the phase of said signals todetermine their phase relationship, and indicating departures of saiddetermined phase relation from said predeter- Vmined multiple phaserelation to indicate departures of said vehicle from said selectedcourse.

2. The method of guiding a vehicle along a selected course whichconsists in simultaneously radiating from spaced locations synchronisedradio waves of different but harmonically related frequencies having axed multiple phase relal tion to each other, separately receiving atsaid vehicle the waves from each of said locations, multiplying thefrequency of one of said separately received waves to provide two radiofrequency signals of identical frequency, comparing the phase of saidsignals to measure their phase relation, determining the multiple phaserelation between said radio waves along said course, adjusting the phaserelation between said signals in accordance with the determination ofsaid multiple phase relation to produce a predetermined phase relationbetween said signals when said vehicle is on said course, and thereafterindicating departures of said measured phase relation of said signalsfrom said predetermined phase relation to indicate departures of saidvehicle from said selected course.

3. The method of measuring the phase relation between two synchronisedradio waves radiated from spaced locations at a point remote from saidlocations which consists in separately receiving each of said waves,amplifying each of said received waves to provide two radio frequencysignals, adding said signals to provide one alternating potential ofradio frequency, subtracting one of said signals from the other toprovide a second alternating potential of radio frequency, separatelyrectifying said alternating potentials to provide corresponding directpotentials, and comparing said direct potentials, whereby a measurementof said phase relation is obtained.

4. A radio beacon for aiding the navigation of a vehicle along aselected course which comprises: a geographically xed radio transmittingsystem including spaced antennae and means for synchronously radiatingfrom said antennae two radio waves of harmonically related frequenciesbearing a fixed multiple phase relation to each other; a pair of radioreceivers on said vehicle for separately receiving said waves; frequencymultiplying means for at least one of said receivers for producing fromsaid receivers a pair of radio frequency signals of like frequency;means for comparing the phase of said signals to determine their phaserelationship; and means for indicating departures of said determinedphase relationship from a predetermined phase relation corresponding tosaid selected course.

5. A device for indicating the phase relationship of two synchronisedradio frequency signals of like frequency comprising: a pair of rectierseach connected in a series circuit with an associated load resistance; afirst supply circuit for applying to one of said rectiers an alternatingpotential proportional to the vector sum of said signals; a secondsupply circuit for applying to the other of said rectiers an alternatingpotential proportional to the vector difference of said signals; meansconnecting said load resistances in series in such manner that directcurrent resulting from rectification of said alternating potentialsflows in opposite directions through said resistances; and means forindicating the direct potential across both of said resistances.

6. A radio beacon for aiding the navigation of a vehicle along aselected course which comprises: a geographically fixed radiotransmitting system including spaced antennae and means forsynchronously radiating from said antennae two radio waves ofharmonically related frequencies bearing a fixed multiple phase relationto each other; a pair of radio receivers on said vehicle for separatelyreceiving said waves; frequency multiplying means for at least one ofsaid re- .including SpaCedantenn era multiplying l means ier; at f l.

means for at least oneo ceivers forqproducing from said; receivers-rapair of radio frequency Asignals of lile gfrequency; means for comparingthephase oisaid signals to .determine theirphase relationship: means forindicating departures oisaid :determined phase relation from apredetermined phase relation; and

means associated rv vitlinrle of saidfreceiyers for shifting thephaseof, one ofgsaid .signals with-reeachother.

7. .A radiobeacon fonaiding thenavigation of a vehicle alonga selectedcoursefwhiehceinprises a geographically 1 dradio transmittingsystemmeans l ier, synchronouslyradiating I n s vd antennaeztwo radiowaves ofharmonieallyrelatedzirequencies bearing a fixed multiple chaserelationtoeach other; v a pair of radio-rco ers. on.-saidyehicle forSeparately receiyinge :waves: frequency t one ci Saidfreceivers forloroducingqfrcln said :receiver s ;a;nair of radio frequency signals of:lise :frequency: means for ,compa-ringing phaseof said signals todetermine their phaserelationship; means for indicating departures of Isaidfdetennined phase relation from a pred etermined;.p l 1: a serela-tion; means associated wi-th; one of. said;v receiyers Vforshifting thevphase yof.one.otsaid signalsl withfrespect to the otheriofsaid signalsan amountfsuiiicient to vbring saidpredetermined-phase;relYtion and said selected coursevintocorrespondencefyvith eachother; andvrneans onisaidvehiclefor supplying to said receivers radio-wavescorresponding in frequency to said radiowaves Iadiatedffr misa-id spacedantennae and havin-g a, know-n -mnltiple phase relation to eachother.

8'. A radio beacon foraidingthe .nayigationof a vehicle along a selectedcoursewhich comprises: a geographically :fixed radio transmitting systemincluding spaced antennaeand means for synchronously radiating fromvsaid antennae two radio waves of harmonically -relatedfrequenciesbearing a fixed multiple phase relationtofeach other; a pairofradioieceiverscn said-vehicle connected to a, receivingantennaforseparately yreceiving said Waves; :frequency imultipiying said receiversfor producing from said receivers-apair of -radio frequency signals oflike frequency; vmeans f cncomparing the phase of saidsignals to`determine their phase relationship;meansor indicating departures of saiddetermined phase relation from a predetermined phase relation; meansassociated with one of said receivers lfor'shifting the phase of one ofsaidsignals withv respect to the other of saidsignals .an.amountsuicient to fbring said predetermined phaserelation and, said selectedcourse into correspondence With each other; generator means on said`vehicle forsupplying .to said receivers radiowayes corresponding infrequency to said radio waves radiated from spaced antennae and havingalmown multiple phase relation to eachother; and means for selectivelyconnecting to said. receivers said receiving antenna, said generator andboth said antenna and said generator.

Y9. A radio reoeiyerincluding two channelsfor separately simultaneouslyreceiying and amplifying two radio waves of different -but harmonicallyrelated frequencies to produce a pair of output signals, means in onechannel forconverting the frequency of the wave received therepy toproduce `an output signal having a fre-:nutcircuits.-luaying;reactances.inrersely .;propor-l tional, to theireduenciescofesaid, alternating;. potentials .and raides .of freactance te resistance Y dire.ctly ;pronortional tothezfredueneielaltern.ating potentials, rneans oo -pl output circuits f ercproducingftwo currents oiglike .fr fluency-corresponding aid alternating :poten s,thephaseirelation be- `tvyeensaid alterna ngfcurrentsecrrespending.tothe multiplenhas el hating potentials, and a 1 means coupled to ;.S.a idVlas vindicating 1 the phase rela frequencyalternatingcurrents- 1 1 Themetnodoi :quency waves of argh/en` duencygrcrn one location,simultaneously radiating from aise ond location spaced .irom/saidoneclocatien-rade reduency fwaves -ofy a @fluency .armonically relatedto said: given;fresuencyfinaintaining a lxed multiplephaserelationbetween midwives, separately :receiving at said i. vehiclethe waves from each Of-said locations, and continuously Y determiningthe instantaneous multiple *..Phase relationbetween the received wavesv1 2. The-method 4oi-iguidinga vehicle along a selected coursewhichfconsists in'` simultaneously radiating from 1 spaced z locationssynchronised radio wavesof v diiterent lout harmonicall-y relatedfrequencies,Y .maintaining anxed multiple phase vrelation between saidwaves to; define a locus of points .of predeterrninedymultipley phaserelation 7between Asaid waves .and coinciding Awith :said A`selected.course, separately-receiying rattsaidivehicle the-Waves from eachof saidlocationscomparing said received Waves determinetheir instantaneousnpiultiplephase relation, and I continuously indicating ydepartures. -ofsaid determined instantaneous multiple phase relation from saidpredetermined multiple phase relation to indicate departures ofsaidvehicle fromsaid selected course. A

13. A radio beacon for vaiding the navigation of a Vehicle along aselected course which comprises: ageographically xed radiotransmittingsystem Vincluding spaced antennae; means Vfor simultaneously 4radiatinglfrom said antennae two radio-waves of different-butharmonically'irelated frequencies vhearing affixed multiple fphasefrela-K tion to-each other; means `on said vehicle for separatelyreceivingisaid vradio1 waves; andfxneans for :continuouslyindicating-departures of-.said determined instananeousrmultiplephasefrelation v*from a predetermined multiple phase relationcorresponding to said senoted-course.

1 4. The-method of measuring:thephese rela tion between--synchrcnizedradio .W es of flierlmcmically reIated frequencies .-whien-.lconsietsseparately' receiving said waves', multiplying the frequency of at leastone of said received waves vto provide radio frequency signals of likefrequency, and continuously 4determining the instantaneous phaserelationbetween-said signals.

15. A device for determining the phase relation of two synchronizedradio waves of different butV harmonically related frequencies,comprising:v two radio frequency receivers each tuned to a different oneof said harmonically related frequencies; a frequency multiplier for atleast one of said receivers adjusted to produce from 'said receivers apair ofsignals of like frequency; and means for continuously comparingthe phase of said signals to determine the instantaneous lphase relationthereof. Y

1 16. A radio beacon for aiding the navigation `ofa vehicle along'aselected course whichlcomprises: a geographically fixed radiotransmitting system including spaced antennae and means forsynchronously radiating from said antennae two radio waves ofharmonically related frequencies-bearing a fixed multiple phase relationto each other; a pair of radio receivers von said vehicle for separatelyreceiving said waves; frequency changing means for at least one of saidreceivers for producing from' said receivers a pair of radio frequencysignals of like frequency; means for comparing the phase of said signalsto determine their phase relationship; and means for indicatingdepartures of said determined phase relationship from a predeterminedphase relation corresponding to said selected course. *Y

17. The method 'of measuring the phase relation between synchronizedradio waves of harmonically related vfrequencies which consists inseparately receiving said waves, changingthe frequency of at least oneof said received waves to'provide radio frequency signals of likefrequency, and continuously determining the instantaneous phase relationbetween said signals.

18. A device for determining the phase relation of two synchronizedradio waves of different but harmonically related frequencies,comprising: two radio frequency receivers each tuned to a different oneof said harmonically related frequencies; a frequency changer for atleast one ofsaid receivers adjusted to produce from said receivers apairof signals of like frequency; and means for continuously comparing thephase of said signals to determine the instantaneous phase relationthereof. l

19. In a radio navigational aid, theV combination of: a radio receiverhaving an input and an output and including two channels lfor separatelysimultaneously receiving and amplifying two radio waves of different butharmonically related frequencies; phase measuring means connected to theoutput of said receiver for continuously determining the instantaneousmultiple phase relation between the receivedv waves; generator meansassociated 4with said receiver for producing two radio frequency signalscorresponding in frequency to said waves and having a known fixedmultiple phase relation to each other; manual control means operable toconnect said generator means to the input of said receiver; and manual.adjustment means coacting with said phase measuring means and operableto vary `the multiple phase relation indicated thereby, wherebyupon-operation Vof said manual control means said adjustment #means maybe operated to bring said indicated 24 multiple phase relation intocorrespondence with said known multiple phase relation.

20. In a radio navigational aid, the combination of: a radio receiverhaving an input and an output and including two channels for separatelyVsimultaneously receiving and amplifying two radio waves of different butharmonically related frequencies; phase measuring means connected to theoutput of said receiver for continuously determining the instantaneousmultiple phase relation between the received waves; manually operablephase shifting means in one of said channels, whereby the operativecondition of said receiver and phase measuring means may be verified byobservation of a shift in the indicated multiple phase relationresulting from operation of said phase shifting means; generator meansassociated with said receiver for producing two radio frequency signalscorresponding in frequency to said waves and having a known fixedmultiple phase relation to each other; manual control means operable toconnect said generator means to the input of said receiver; and manualadjustment means coacting with said phase measuring means and operableto vary the multiple phase relation indicated thereby, whereby uponoperation of said manual control means said adjustment means may beoperated to bring said indicated multiple phase relation intocorrespondence with said known multiple phase relation.

21. In combination: a first transmitting station for radiating a wave ofa given frequency; a relay station spaced from said first station forradiating a wave of a different but harmonically related frequency, bothof said waves being derived from a common source; means for establishinga fixed pattern of multiple phase 1- difference in space, said meansincluding a receiver located at a fixed position and receiving signalsfrom both of said stations, means coupled to said receiver for providinga control signal having a value dependent upon the multiple phaserelation of the received signals, and a phase control means coactingwith at least one of said stations and responsive to said control signalin such sense as to oppose any deviation from a predetermined multiplephase relation between said-waves; a mobile receiver comprising areceived antennafa first channel coupled to 'said antenna forV receivingsignals of said given frequency, a second channel coupled to saidreceiving antenna for receiving signals of said different frequency,,means for producing 'from the outputs of said two channels two signalsof like frequency, and a phase indicator controlled by said likefrequency signals and providing an indication dependent upon themull'tiple phase relation of the two received signals;

generator means at said mobile receiver for generating a distortedsignal having. standardizing harmonic signal components of said givenfrequency and of said different frequency, said standardizing harmonicsignal components bearing a fixed and known multiple phase relation toeach other; switching means for transferring the inputs of said firstand second channels from y said receiving antenna towsaid generatormeans;

and a manually adjustable means for adjusting said phase indicator to apredetermined fixed indication when said switchingvmeans connects saidinputsy to said generator'means, thus correlating the indications ofsaid phase indicator with said known and fixed multiple phase relationand allowing Vsaid indicator 'to give true indications of the multiplephase relations between the received signals when said switching meansconnects said inputs to said receiving antenna.

22. In a radio navigational system, the conibination of a pair of spacedtransmitting stations for radiating two radio frequency signals ofunlike but harmonically related frequencies; a dual channel receiver ata fixed position for separately and simultaneously receiving saidsignals to produce an output signal from each of said channels, themultiple phase relation between said output signals bearing a fixedrelation to the multiple phase relation between the received signals;phase responsive means actuated by both of said output signals forproducing a control voltage the magnitude and sign of which isrepresentative of the multiple phase relation between said outputsignals; a phase change means coacting with at least one of saidtransmitting stations and operable to vary the multiple phase relationbetween said radio frequency signals; means coupled to said phaseresponsive means and responsive to variations of said control voltagefor operating said phase change means to maintain a predetermined fixedmultiple phase relation between said radio frequency signals; a mobilereceiver including means for indicating the difference in the distancesof said mobile receiver from said transmitting stations as representedby the diierence in the transit times from said stations to said mobilereceiver, said last mentioned means including an indicating device forindicating changes in the time phase relation of two input signals ofthe transmitted frequencies; a receiving antenna; a signal generator forproducing a pair of standard signals having the same frequencies as saidradio frequency signals and having a known Xed multiple phase relationto each other; manually operable switching means having a rst positionconnecting the input of said mobile receiver to said receiving antennaand having a second position connecting the input of said mobilereceiver to said signal generator; and means for adjusting saidindicating device to a given indication corresponding to said known xedmultiple phase relation when said switching means is in said secondposition to thereby insure that the indications given by said indicatingdevice accurately correspond to said diiferences in the distances fromsaid mobile receiver to said transmitting stations when said switchingmeans is in said rst position.

23. In combination: a pair of spaced transmitting stations for radiatingsignals of unlike but harmonically related frequencies; means formaintaining a xed multiple phase relation between said radiated signalscomprising a receiver responsive to said signals for producing an outputcurrent representative of the multiple phase relation between saidreceived signals and a phase shift means coacting with said receiver andat least one of said transmitting stations and responsive to variationsof said output current for producing a phase shift in the radiatedsignal of the opposite sense to that indicated by the variations of saidoutput current; a mobile receiver having an antenna for receiving saidsignals from said transmitting stations and including two channels forobtaining from the received signals a pair of like frequency outputsignals; and a phase comparison circuit connected between the outputs ofsaid channels and responsive to said output signals, said phasecomparison circuit including a phase indicator for continuouslyindicating the multiple phase relation of the received signals at saidantenna.

WILLIAM J. OBRIEN.

REFERENCES CITED The following references are of record in the flle ofthis patent:

